Method of and apparatus for coating metallic strands with a metal coating



Oct. 24, 1950 K. G. COBURN METHOD OF AND APPARATUS FOR COATING METALLIC STRANDS WITH A METAL COATING Filed Feb. 15-, 1945 3 wuc/MM KENNETH G. COBURN Patented Oct. 24, 1950 7 METHOD OF AND APPARATUS FOR COAT- ING METALLIC STRANDS WITH A METAL COATING Kenneth G. Coburn, Middletown, Ohio, assignor to Armco Steel Corporation, a corporation of Ohio Application February 13, 1945, Serial No. 577,656

' 12 Claims. (01.117-1-14) My invention relates to problems involved in. the coating of continuous metallic strands such,

for example, as iron or. steel wire or strip, with protective metals by hot dipping. I shall describe my invention in. an exemplary embodiment having to do with the coating of iron wire with aluminum, it-being understood that the utility of my invention is not confined to the exemplary embodiment.

It has long been understood that at the place where the metallic strand emerges from the bath of molten metal it" is necessary not only to keep the surface of the bath free from oxides, dross and other impurities, but also, with highly oxidizable metals, to prevent the formation of oxides on the coated strand between the time of its emergence from the bath and the time when the strand and its coating shall have cooled below a temperature at which. oxides will form. Concurrently, it is necessary to make some provision for controlling the thickness and other characteristics of the coating itself.

For the latter purpose, exit rolls or wipers are sometimes used; but with some metallic coating substances, their use has not been successful.

In the coating of galvanized iron, it is a conventional practice to protect the surface of the metal bath from oxidation by maintaining a mixture of charcoal, flux and water thereon, through which. the wire emerges. In the coating of wire with aluminum, however, no combination of these or other ingredients has been found which willv notdecompose due to the heat of the bath, or which will not remain too viscous to do a'satisfactory fluxing and cleaning job. i

It has been suggested that the exit end. of a metal coating bath be protected with fl an, inert ornon-oxidizing atmosphere not only to prevent the formation of oxides, butv also to permit the The principal objects of my invention are the provision of solutions to the problems which have just been indicated. It is an object of my inven tion .to provide apparatus for the purpose set forth which is simple in construction, inexpenprocedure of which I shall now describe the aforesaid exemplary embodiment. Reference is made to the accompanying drawing wherein I have shown diagrammatically in section the essential features of the exemplary embodiment.

In the drawing I have indicated diagram- ;matically a coating pot l in which a bath of the molten coating metal 2, e. g., aluminum, is

maintained in melted condition by suitable heating means not shown but readily understood by those skilled in the art. In the simplest form of my apparatus, a metal strand 3, for example a wire, is passed into the bath and around a sheave 4 or other direction changing device, so that it can be caused to emerge from the bath in an upward direction. The actual angle of emergence is not a limitation upon my invention.

I cause the strand} to passthrough a tube, hood or standpipe 5 after it emerges from the bath 2. The shape of this standpipe will be appropriate to the shape of the strand being coated, and it is desirable that the strand be able to pass freely through the standpipe without touching it. When coating a single wire, a, piece of ordinary pipe of appropriate size may be employed and of such complex apparatus, its action has not been perfect. It is difiicult to maintain continuously in a closedhood or standpipe a satisfactory inert or reducing atmosphere: Moreover, 7

tend to accumulate in the hood or standpipe-,-

may besupported above the bath in any suitable way.

The pipe 5 is provided with two branch lines, as shown- A larger branch line 6 is joined to the pipe near its lower end, while a smaller one, 1,.joinsit at a point farther from its lower end. Both of the branch lines 6 and I join the main pipe 5 at anacute angle and are directed downwardly, as indicated. The exact angularity, indicated at 8 and 9, may be considerably varied. In practice I am employing an angle of about 30.

The. upper or smaller branch line 1 is employed to introduce air into-the standpipe 5.

Low pressure reducing gas is introduced through .thelower and larger branch line 6. The purpose of the. downward inclination of the branch lines as they join the standpipe 5 is to utilize the pressures of the gas and air (particularly the latter,

ing bath. This permits the greater part of the gas-air mixture to escape from the lower end of the standpipe.

Dimensions are not a limitation upon my invention; but as a guide to the skilled worker, I may say that in one installation for coating a single wire with aluminum, the standpipe 5 is a piece of l-in. tubing, 2 ft. in length. Its lower end is supported about T g-in. above the surface of V the bath. The branch line I is made of %-in.

pipe and enters the standpipe 5 at a point about 4V2-in. below its upper end. Th branch line 6 ismade of %in. pipe and enters the standpipe 5 about 4'V -in. from its lower end. It will be understood that these dimensions are exemplary and may not only be widely varied, but may advantageously be varied in relationship to the speed of passage of the strand, the pressure of the air, and the kind and pressure of the gas. When a plurality of wires are to be-coated in parallel, a plurality of standpipes may be used or a single hood dimensioned to contain all the wires may be substituted. Where strip material is being coated, the hood or standpipe will, of course, be increased in one transverse dimension to accommodate the width of the strip; and where the strip acts to divide such a hood or standpipe in such fashion that'gas circulation about the edges of the strip is impeded, it is within the purview of my invention to connect with the hood two or more branch lines on each side of the strip.

One purpose of my apparatus is to maintain about the emerging strand and over the bath at the point of emergence an atmosphere which is non-oxidizing, semi-reducing or reducing in character to restrict the formation of oxide on the surface of the bath and permit the strand to emerge through a clean area substantially free from oxides. The gas introduced through the branch line 6 will be preferably a reducing gas, and is of combustible character. Of such gases, hydrogen, cracked ammonia, carbon monoxide and natural or artificial gases containing hydro gen or carbon monoxide are exemplary; The relative quantities of gas and air can be altered to control the reducing character of the gas-air mixture and in this way variations in the appearance of the coating may be achieved.

The gas-air mixture is adjusted so as to be combustible but non-explosive. The quantity of the gas-air mixture may likewise be adjusted to control the volume of flow through the standpipe. I have already indicated that the principal flow of gas or gas-air mixture through the standpipe is in the downward direction. The emerging coated strand is thus bathed in a descending flow of gas, assisting in the drainage of molten coating material from the strand, and promoting the formation of a smooth and controlled coating.

The gas-air mixture should burn at the bottom opening of the standpipe, as indicated at Ill. The extra temperature produced by this flame at the extreme surface makes the coating and probably any oxide present more fluid and has been found to result in a thinner and'smoother coating. Such a coating is free from those heavy spots which in other procedures tend-to occur 4 along the length of the wire and are commonly known as berries. The burning of the gas at the lower end of the standpipe results, of course, in a substantial gas expansion and more effectively prevents oxygen infiltration into the standpipe and keeps it away from the surface of the bath at the point of emergence. Again, the increased velocity of the expanding gases acts to keep any floating oxide particles swept away from the standpipe and. the emerging strand.

I preferably so adjust the volume and flow of my gases that there is a slight gas exit at the top of the standpipe where, for safetys sake, the gases are permitted to burn, as at H. Again, the expanding gases, due to the combustion, serve to impede oxygen infiltration; and by maintaining flames both at the top and at the bottom of my standpipe or hood, I am enabled to be sure at'all times that the standpipe or hood is kept filled with the desired atmosphere, and to detect and prevent such maladjustment of pressures and flow as would result in the aspiration of air into the top of the standpipe.

While I have spoken of theupper branch line 1 as an inlet for air, and while air will ordinarily be used, it should be understood that other gases may be employed instead; For example; a neutral diluent such as nitrogen may be introduced through the tube 1, a combustible reducing gas being introduced through'the tube 6. In the specific apparatus, I .have found it both convenient and economical to introduce a combustible reducing gas at relatively low pressure through the tube 6 while employing the tube 1 for the introduction either of air or of a neutral gas at substantially higher pressures to insure the downward flow. The use of a jet of gas at higher pressure introduced near the upper end of the standpipe in a downwardly direction is useful to produce the downward flow; but this gas may be derived from the same-source and be of the same kind as the gas introduced through the tube 6 if pressures are'properly controlled. Indeed, it is possible to provide but one branch line and introduce through it a reducing gas or combustible reducing gas mixture, providing pressure and rate of flow can be correctly adjusted to produce the required downward flow.

- The manner in which the strand 3 is treated prio to its entry into the coating bath 2 forms no limitation upon my invention and I have not illustrated any pretreatment. I have, for. example, employed my apparatus and method in connection with strand material pretreated in accordance with the teachings of the Sendzimir Patent 2,110,893, but other modes'of preparing the strand for coating ma be followed.

A temperature of 1250 to 1300 F. is my preferred bath temperature when coating strand material'with aluminum or aluminum alloy in practicing this invntion' When coating with other materials, the temperature of the bath will, of course, be appropriately varied. But through the use of my invention, I have produced smoothly and uniformly coated wire where the coating is free of inclusions and of discontinuities without the use of exit rolls, wiping means, exit fluxes or other expedients to eliminate oxides and control coating thicknesses. It will be understood that the thickness of coating may be varied in my procedure in various ways, as by altering the speed ofpassage of the strand through the bath, altering the temperature and altering the volume of the downward flow of gas through the stand- V "Modifications may be made in myinventio'n without departing from the spirit o'f'it Having thus described my invention-,'What-I"claim as'n'ew and desire to secure by Letters-Patent is:

IJIna-pparatus for-coating metal strands by hotdipping, a vessel" in which abathof molten coating metal maybe maintained, means'dor passing a metal strand'into said bath and causing it to emerge therefrom, an elongated tube dimensioned to surround the strand in its path of emergence from the bath so that saidstrand may pass freely through said tube, means to position said tube so that it is open to the atmos phere at both ends, an end of said tube adjacent said bath being located in spaced relation from the bathsurface to permit escape of gases against thesuriace of said bath, means forintroducing into said tube a controlled gaseous atmosphere, and means for producing in said tube a movement of said atmosphere primarily towardfsaid bath.

,2. In apparatus for coating metal: strands by hot dipping, a vessel in which a bath of molten coating metal may be maintained, means for passing a metal strand into said bath and causing it to emerge therefrom, an elongated tube dimensioned to surround the strand in its path of emergence from the bath so that said strand may pass freely through said tube, means to position said tube so that it is open to theatmosphere at both ends, an end of said tube adjacent said bath being located in spaced relation from the bath surface to permit escape ofg gases against the surface of said bath at the bath surface, and means for introducing into said tube'a controlled gaseous atmosphere, and means for producing in said tube a movement of said atmosphere primarily toward said bath, said last mentioned means comprising a branch conduit joining said hood at an acute angle and directed toward said bath. r

3. In apparatus for coating metal strands by hot dipping, a vessel in which ajvbath of molten coating metal may be maintained, means for passing a metal strand into said'bath and causing it to emerge therefrom, an elongated tube dimensioned to surround the strand in its path of emergence from the bath, so that'said strand may pass freely through said tube,-means to position said tube so that it is open to the atmosphere at both ends, an end of said tube adjacent said bath being located in spaced relation from-- the bath surface to permit escape of gases against the surface of said bath, means .for introducing into said tube a controlled gaseous atmosphere, and means for producing in said tube a move ment of said atmosphere prirnarilytoward said bath, said last mentioned means comprising a branch conduit joining said hood at an acute angle and directed toward said bath, said branch conduit being a passageway for combustible reducing gas, there being a second branch conduit of smaller diameter connected to said tube at a point more remote from the end-thereof adjacent said bath and also directed toward said bath at 6 hood having an'en'd approaching said bath but terminating short of the surface thereof, means for maintaining in said hood an atmosphere of controlled character, and means for causing said atmosphere to move within said hood primarily toward said bath so that a substantial quantity oisaid atmosphere escapes from said lower end of said hood.

' 5. In combination with a container fora bath of molten coating metal through which a metallic strand to be coated'is passed, a hood freely surrounding said strand after it has emerged from said bath, said hood being of elongated tube-like form with open ends, one of said ends approaching'but maintained out of contact with the surface of. said bath so as to provide a narrow-orifice for gas escape, at least one conduit connected to said hood at an acute angle and directed as it approaches said hood toward said bath,said conduit'being for the introduction of combustible reducing gas into said hood and for producing aflow of said gas therein toward said bath, so that said gas escapes from said orifice where itmay be burned against the surface of said bath.

6. In combination with a container for a bath of molten coating metal through which a metallic strand to be coated is passed, a hood freely surrounding said strand after it has emerged from said bath, said hood being of elongated tube-like form with open ends, one of said ends approaching but maintained out of contact with the surface of said bath so as to provide a narrow orifice for gas escape, at least one conduit connected to said hood at an acute angle and directed as it approaches said hood toward said bath, said conduit being for the introduction Of combustible an acute angle to said tube, said last mentioned metallic strand to be coated may be passed and from which it may be withdrawn substantially vertically, a vertical hood supported above said bath to surround the path of travel of said strand after it has emerged from said bath, said reducing gas into said'hood and for producing a flow of said gas therein toward said bath, so that said gas escapes from said orifice where it may be burned against the surface of said bath, and a second similarly directed conduit connecting with said hood at a point more remote from said bath for the introduction of additional gas.

7. A process of coating metallic strands with molten coating metal which comprises passing a strand through a bath of molten coating metal and withdrawing it therefrom upwardly in a path of travel within an elongated hood having open ends, passing the strand freely through said hood, supporting said hood so that one of its open ends lies close to but above and out of contact with the bath to leave a gas passage orifice, filling said hood with a controlled, combustible gaseous atmosphere and producing in said. hood a movement of said atmosphere in part at least toward said bath whereby some of said atmosphere escapes from an orifice formed between said end of the hood and the surface of said bath, and burning said atmosphere as it issues from the said orifice.

8. The process of claim 7 wherein the said gas is also burned as it issues from the opposite end of said hood.

9. The process of claim 7 wherein the movement of gas in said hood is produced by directing gas thereinto under pressure at an acute angle to the axis of said hood and toward said bath.

10. The process of claim 7 wherein the'movement of gas in said hood is produced by directing gas thereinto under pressure at an acute angle to the axis of said hood and toward said bath, while introducing into said hood at a point more remote from said bath a quantity of air enact-as;

under pressure and directed -tolproduce said flow of gas toward said bath. 11, The process of claim 7 wherein the move: ment of gas in said hood is produced by directing gas thereinto under pressure at an acute ane gle to the axis of said hood and toward said bath, while introducing into said hood at a point more remote from said bath a quantity of, air under pressure and directed to produce said now of gas toward said bath, and adjusting the pressure and volume of the gas and air so that some of the gas-air mixture escapes from an end of said hood remote from said bath and is there burned.

12. A process of treating hot coated metal strands to produce more perfect coatings thereon which consists in surrounding a strand as it emerges from a molten coating bath with ahood through which the strand freely passes without contact, said hood being of elongated form and open at both ends, one of said ends approaching but slightly separated from the surface of said bath so as to form a gas escape orifice surrounding the point of emergence of the strand from the bath, and maintaining within said hood a moving atmosphere including combustible reducing gas while directing the movement of said gas principally toward said bath so that the greater part of it escapes from the said orifice while some of it escapes from the opposite end of said hood, and burning the said gas at both escape points whereby to produce gas expansion and prevent infiltration ofouter air into the hood.

KENNETH G. COBURN.

REFERENCES CITED UNITED STATES PATENTS Number t' Name Date 1,673,624 Howe June 12,1928 2,010,941 Bradley Aug. 13; 1935 2,034,348 "Lytle Mar. 17, 1936 '2 ;097,472 'Schueler Nov. 2, 1937 2,166,249 Herman July 18, 1939 2,197,622 Sendzimir Apr. 16, 1940 2,332,978 Ahern Oct. 26, 1943 

7. A PROCESS OF COATING METALLIC STRANDS WITH MOLTEN COATING METAL WHICH COMPRISES PASSING A STRAND THROUGH A BATH OF MOLTEN COATING METAL AND WITHDRAWING IT THEREFROM UPWARDLY IN A PATH OF TRAVEL WITHIN AN ELONGATED HOOD HAVING OPEN ENDS, PASSING THE STRAND FREELY THROUGH SAID HOOD, SUPPORTING SAID HOOD SO THAT ONE OF ITS OPEN ENDS LIES CLOSE TO BUT ABOVE AND OUT OF CONTACT WITH THE BATH TO LEAVE A GAS PASSAGE ORIFICE, FILLING SAID HOOD WITH A CONTROLLED, COMBUSTIBLE GASEOUS ATMOSPHERE AND PRODUCING IN SAID HOOD A MOVEMENT OF SAID ATMOSPHERE IN PART AT LEAST TOWARD SAID BATH WHEREBY SOME OF SAID ATMOSPHERE ESCAPES FROM AN ORIFICE FORMED BETWEEN SAID END OF THE HOOD AND THE SURFACE OF SAID BATH, AND BURNING SAID ATMOSPHERE AS IT ISSUES FROM THE SAID ORIFICE. 